Erosion protection for wells



Oct. 1, 1968 A. v. METLER 3,403,732

EROSION PRQTECTION FOR WELLS Filed March 30, 1966 2 Sheets-Sheet 1 ALVIN V. METLER INVENTOR ATTORNEY Oct. 1, 1968 A. v. METLER 3,403,732

EROSION PROTECTION FOR WELLS Filed March 50. 1966 2 Sheets-Sheet ALVIN V. METLER INVENTOR ATTORNEY BY Mam; I

United States Patent 3,403,732 EROSION PROTECTION FOR WELLS Alvin V. Metler, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Mar. 30, 1966, Ser. No. 538,629 4 Claims. (Cl. 166-242) ABSTRACT OF THE DISCLOSURE An assembly for protecting the surface of a tubing carrying fluid from a lower formation in a multiply completed well from the erosive eifects of a fluid entering the well from a higher formation including a casing having perforations adjacent the higher formation. The perforations are positioned so that the streams of fluids entering through the perforations will intersect each other before impinging on the surface to be protected. By allowing the streams to intersect, turbulent flow is created and the kinetic energy of the fluid is decreased thereby reducing the erosion of the tubing.

This invention relates to the production of subterranean fluids through wells, and more particularly to a method and apparatus for alleviating erosion of downhole well equipment by detrital material contained in such subterranean fluids.

In the petroleum industry, downhole well equipment often is subjected to erosion due to the abrasive action of detrital material such as unconsolidated sand grains entrained in petroleum fluids as they enter the well. This problem most often is encountered in multiply completed wells which product fluids from two or more levels in a well- The most common multiply completed wells are dual-completion wells in which oil or gas is produced from two vertically spaced subterranean formations. A conventional manner of dually producing such formations is to set and cement casing through both formations and then set a casing packer between the formations. A tubing string is extended through the packer with its lower open end landed adjacent the lower productive formation. The casing packer thus effectively seals off the annular space between the tubing and casing and isolates the lower formation, which is in fluid communication with the interior of the tubing string. The fluid from the lower formation thus flows through the tubing and to the surface of the well or wellhead separately from the fluid from the upper formation which is produced through perforations in the casing into the annulus between the casing and the tubing string. The fluid from the upper formation flows to the wellhead either directly through the annulus or through an additional tubing string.

Another form of dual-completion well is the so-called slim hole dually completed well. In this arrangement the well is not cased in the conventional manner and two parallel strings of tubing or small casings are cemented in the well. Each tubing string is perforated selectively at the level of one of the subterranean formations and each formation is produced separately through its respective tubing string.

In either form of multiple completion, a section of pipe such as well tubing extends past a productive formation and thus is exposed to the produced subterranean fluid as it enters the well either through perforations in the wall of the casing, as in the first above-described arrangement, or through the perforations in the wall of the tubing itself, as in the second above-described arrangement. The fluid usually is under substantial pressure and passes from the productive formation through the restricted perforations in the casing or tubing at a high velocity and in jetted streams. This particularly is true where the fluid 3,403,732 Patented Oct. 1, 1968 being produced is comprised primarily of gas. Such fluid often has a content of sand or other particulate detrital material which impinges against the pipe surface adjacent the perforations. Such detrital material entrained in the incoming fluid abrades and erodes the pipe surface, thus leading to pipe failure, and also intensifying the corrosion of the pipe.

In the past, numerous means have been employed in attemptsto protect tubing surfaces and alleviate the erosion thereof. One technique involves the wrapping of layers of lead around the tubing on the theory that a malleable material would absorb some of the kinetic energy of the detrital material more readily than the tubing itself. Alternatively, hard, brittle material such as ceramics and glass and resilient materials such as rubber have been employed as protective materials for the tubing. While such techniques have met with some success, the resilient coatings usually being the most efl ective, none of these techniques have proven entirely satisfactory.

One difliculty experienced with the heretofore-practiced procedures resides in the fact that the materials used, even though sometimes more resistant to the abrasive action of the detrital material than the metal pipe surfaces, still experience some erosion and ultimately fail, leaving the pipe surfaces exposed. This of course necessitates expensive workovers such as withdrawing the tubing, repairing it if necessary, and providing additional protective material.

In accordance with the instant invention, there is provided new and improved apparatus for alleviating erosion of downhole well equipment and which does not require the disposition of protective members intermediate the casing perforations and the surface within the interior of the casing which is to be protected from erosion.

In carrying out the present invention, there is provided a well traversing a subterranean formation from which it is desired to recover fluids such as petroleum gases. The well has a conduit therein with a plurality of perforations opposite the formation through which the produced fluid is flowed into the interior of the conduit. The fluid emanates from the perforations in the form of jetted streams and has entrained therein abrasive detrital material. In accordance with the instant invention, the paths of at least some of the fluid stream are controlled such that they contact one another to produce turbulence at the point of contact thereof and deflection of the entrained detrital particles. Thus, any detrital material impinging upon the tubing or other surface does so usually at an oblique angle and at a reduced kinetic energy level with the result of relatively little erosion of the tubing surface.

In a preferred embodiment of the invention, the perforations in the conduit are located in a first semiperipheral sector extending about the conduit. The outermost of these perforations defines a blank second semiperipheral sector of the conduit which extends longitudinally through the perforated interval. The perforations in the conduit define linear flow courses for the flow of fluids into the interior of the conduit and are disposed such that at least one of the flow courses is oriented at an oblique angle relative to a surface within the conduit for which it is desired to provide erosion protection and intersects another of the flow courses.

In yet another embodiment of the invention, a second conduit of a size smaller than the first conduit above described is eccentrically disposed within the first conduit and extends longitudinally through the perforated interval of the first conduit adjacent the aforementioned blank sector thereof. Thus, the second conduit surface is relatively remote from the perforations through which the gas or other fluid is produced into the interior of the well. In one form of this embodiment of the invention,

the perforations are arranged in a plurality of groups which are spaced longitudinally along the first conduit. Each of the perforations of a group is disposed in a common horizontal or transverse plane and each of the flow courses defined by the perforations of such a group is intersected by another of the flow courses at a point interiorly of the first conduit but exteriorly of the second conduit.

For a better understanding of the present invention, reference may be made to the following detalied description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevation partly in section of a well embodying one form of the present invention;

FIGURE 2 is a cross-sectional view taken along line 2-2 of FIGURE 1;

FIGURE 3 is an elevation partly in section showing a well embodying another form of the invention; and

FIGURE 4 is an elevation partly in section illustrating a well embodying yet another form of the invention.

With reference to FIGURE 1, there is shown a wellbore traversing a productive formation 12 and provided with a first conduit or casing string 14. The casing is cemented as indicated by 15 and the casing and surrounding cement sheath are provided with a plurality of perforations generally indicated by reference numeral 16 and disposed in accordance with the instant invention as described in detail hereinafter. A packer 19 is disposed between the productive formation 12 and a lower productive formation (not shown) in order to isolate these formations from one another so that there is no communication between these formations within the well. A production tubing string 20 is disposed in the well as illustrated and extends from the wellhead 21 and is landed at a level (not shown) below the packer 19, usually adjacent the lower productive formation. Fluids from the lower productive formation thus are produced through the interior of the tubing string and carried to the surface of the well where they pass into a suitable gathering line 20a. The section of the tubing string 20 opposite the perforated interval in the casing is offset in accordance with the instant invention as described in greater detail hereinafter.

A second packer 22 is provided between the tubing string 20 and the casing 14 at a point above the top of the productive formation 12. A second tubing string 24 extends from the surface of the well and through the second packer 22 as shown. As is apparent from the drawing, the second tubing string 24 provides a production passage to the surface of the well or wellhead for the fluids produced from the productive formation 12. At the well head. fluids from tubing string 24 are delivered into a gathering line 24a.

The production equipment thus far described is conventional and does not by itself comprise the present invention. Also, it will be understood that the arrangement thus far described is exemplary only and that other suitable arrangements may be used. For example, tubing 24 and packer 22 may be dispensed with and fluids from the productive formation 12 may be produced to the surface of the well directly through the annular space defined by the tubing 20 and the casing 14. Alternatively, tubing string 20 may not extend to the wellhead, but instead may terminate within or above packer 22, in which case fluid from the lower formation will pass from tubing 20 into the space between tubing 24 and casing 14 and thence upwardly to the wellhead. Also, while only a single casing string 14 is shown, it will be understood that the well may be provided with a plurality of casing strings. For example, the well may be provided with a suitable conductor pipe or surface string and one or more intermediate strings as will be understood by those skilled in the art. In addition, while the casing 14 in FIGURE 1 is shown as extending completely to the surface of the well, it will be understood that other suitable arrangements may be used. For example the perforated outer conduit may take the form of a liner which is suspended from or otherwise extends into a casing string. Also, the perforated conduit may take the form of a so-called scab liner which does not extend up into a casing string but simply rests upon the bottom of the borehole and is cemented therein in accordance with conventional practices. In this case, all or part of the well above the perforated liner may be uncased. Such completion practices are well known to those skilled in the art and therefore will not be described further.

In accordance with the instant invention, the perforations 16 opposite the productive formation 12 are disposed such that the several jetted streams emanating therefrom contact each other before they contact the outer surface of tubing 20. In addition, the section 20b of tubing 20 opposite the perforations is eccentrically disposed within the well adjacent a blank sector of the conduit 14 outlined by the perforations. This orientation of the perforations in the casing and the inner production tubing can best be seen in FIGURE 2.

With reference to FIGURE 2 there is shown a plurality of perforations 2833 which are disposed in a common horizontal plane extending transversely of the wellbore. The perforations 28-33 define a plurality of linear flow courses 28a-33a, respectively, each of which intersects another flow course before it intersects, if at all, the outer surface of tubing 26. By the term flow course as used herein and in the appended claims is meant that space enclosed within an extension of a perforation interiorly of the Well conduit. For example, assuming perforation 28 to be a cylindrical opening, as usually will be the case, flow course 28a will be defined by an imaginary cylinder extending into the interior of the conduit from the perforation 28 and coaxially therewith. While the fluid passing through the perforations and into the interior of the conduit actually will flow somewhat radially from the perforations, it will be recognized that most of the fluid emanating from a given perforation will generally follow its respective flow course. It further can be seen from FIGURE 2 that all of the perforations 28-33 are confined within a first semiperipheral sector 34 of the conduit 14 and that the outermost perforations 28 and 33 within this sector define or outline a blank second semiperipheral sector 36. This same relationship holds true for the groups of perforations above and below the perforations 28-33 so that the blank semiperipheral sector of the conduit extends longitudinally through the perforated interval. The interior of the conduit 14 adjacent this blank sector provides a quiescent zone through which the section 20b of tubing 20 extends. Thus, the tubing 20 is not subject to the abrasive action of the detrital material entrained within the incoming fluids.

As noted above, the section 20b of tubing 20 opposite the perforated interval is eccentrically disposed within the casing 14 and extends through the perforated interval adjacent the blank sector 36 of the casing. Preferably, the outer diameter of section 20b is less than one-half the inner diameter of casing 14 as shown so that the perforations may extend radially through the wall of the casing and still provide for intersection between their respective flow courses at a point interiorly of the casing, but exteriorly of the production tubing. As the jetted streams emanating from the perforations impinge upon one another, fluid flow is converted to turbulent flow and the entrained detrital particles are deflected. Thus, those particles which strike the outer surface of the tubing do so at a much reduced kinetic energy level.

The peripheral spacing of the perforations in a common horizontal plane will depend upon the size of the inner and outer conduits and the size and number of perforations desired. If there is desired only two perforations at a single level within the well, such perforations may be located at diametrically spaced positions in the outer conduit. With only three such perforations, they may be spaced about the casing at intervals of 120 degrees. Regardless of the number of perforations in a common horizontal plane, such perforations preferably are disposed such that at least some of their respective flow courses intersect one another at an angle greater than 90 degrees so that there are at least some force components acting against one another. In a preferred embodiment of the invention, the angle of intersection between at least someof the flow courses is at least 120 degrees.

Turning now to FIGURE 3, there is shown an alternative form of the invention embodied within a dually completed well of the so-called slim hole type. With reference to FIGURE 3, there is shown a borehole 40 which extends from the surface of the earth and traverses a subterranean productive formation 42 and a lower formation (not shown). The borehole 40 contains at least two parallel production strings or flow tubings 44 and 46 which are cemented within the hole by means of cement 48. In the installation illustrated, pipe string 46 is completed for the production of fluids from formation 42 and pipe string 44 is completed for the production of fluids from the lower formation. Thus, fluids from the productive formation 42 flow upwardly through the interior of string 46 to the wellhead 49 where they are passed into a suitable gathering line 46a and production fluids from the lower formation pass upwardly through the interior of string 44 where they are likewise passed to a suitable gathering line 44a. The flow tubing 46 is provided with a plurality of perforations generally indicated by reference numeral 50 through which fluid enters from the productive formation 42 and which are oriented in accordance with the instant invention as described hereinafter.

In well completions of the type illustrated in FIGURE 3, the predominant erosion problem is due to the impingement of detrital material against the inner surface of the pipe string opposite the perforations therein. That is, as will be apparent from an examination of FIGURE 3, the surface generally indicated by reference numeral 54 is subject to erosion due to the abrasive action of detrital material entrained in fluids as they pass through the perforations into the interior of pipe string 46. It often is difficult due to the relatively small size of the flow tubing and its position within the wellbore to perforate the flow tubing at a plurality of locations within a single horizontal plane. In accordance with another embodiment of the instant invention, there is provided an arrangement in which the perforations may be vertically spaced from one another and still oriented such that the fluid streams entering the flow tubing contact one another to produce turbulent flow and deflection of the entrained detritus.

More particularly, and with reference to FIGURE 3, there is provided a plurality of vertically spaced perforations 55-60 oriented such that their respective flow courses 55a60a intersect one another before intersecting the opposed interior surface 54 of flow tubing 46. For example, from an examination of FIGURE 3 it can be seen that the flow course 55a of perforation 55 intersects the flow course 56a of perforation 56 at a point interiorly of the conduit 46 and spaced from the inner surface thereof. Thus, at this point of intersection turbulent flow is produced as described beforehand and the detrital particles which contact the inner tubing surface do so at a much reduced kinetic energy state.

Even in the absence of the interaction between the flow streams of adjacent perforations, fluid flowing through a given perforation such as perforation 56 would simply by virtue of its orientation contact the inner surface 54 of flow tubing 46 at an oblique angle. The abrasive action of the entrained detrital material thus would be much less than if the perforation were oriented such that the fluid flow emanating therefrom contacted the opposing surface at a normal angle. In view of the oblique orientation of the perforations, intersection between the respective flow courses is not absolutely necessary. Thus, in accordance with the broad aspect of the invention, the

flow tubing 46 need only be provided with perforations oriented such as those indicated by reference numerals 56, 58, and 60, with or without the provision of additional intersecting perforations such as 55, 57, and 59. While an arrangement which does not provide for intersection between flow courses usually will not be preferred, it can be seen that erosion of the opposing inner tubing surface will be much less than for those conventional arrangements in which the perforations are oriented at an angle normal to the tubing surface. Such an arrangement may be utilized for example where the relatively precise location and orientation of perforations necessary for the intersection of their respective flow courses is not practical.

Turning now to FIGURE 4, there is shown yet another embodiment of the invention. The assembly shown in FIGURE 4 is similar to that shown in FIGURE 1 and like elements in FIGURE 4 are designated by the same reference numerals as used in FIGURE 1. In FIGURE 4 there is shown a plurality of perforations 70-73 which are oriented at an oblique angle relative to the longitudinal axis of casing 14 similarly as the perforations illustrated in FIGURE 3 and which define a plurality of intersecting flow courses 70a-73a. As in the embodiment of FIGURE 3, this arrangement of perforations may be used where it is not practical or desirable to provide a plurality of perforations lying in a common plane. For example, the embodiment of FIGURE 4 may be advantageously utilized in an installation in which the outer diameter of the production tubing is at least one-half the inner diameter of the casing.

Quite apart from the interaction between the several streams emanating from the perforations, it will be recognized that the remote placement of the tubing section 20b in itself results in substantially reduced erosion of the tubing surface. For example, even if the fiow course 71a in FIGURE 4 were not intersected by another flow course, it can be seen that though the fluid stream emanating from perforation 71 would contact the tubing surface, the entrained particles would strike this surface at a lower energy state than if the conduit were disposed concentrically in the casing and therefore in much closer proximity to the perforation. Preferably, however, flow courses which intersect the tubing are first intersected by another flow course at a point interiorly of the casing, but exteriorly of the production tubing as shown.

Having described certain specific embodiments of the instant invention, it will be understood that further modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.

What is claimed is:

1. In a well penetrating a subterranean formation and adapted for the production of fluids therefrom, an assembly for alleviating erosion of downhole equipment comprising:

a conduit disposed in said well;

a plurality of perforations in an interval of said conduit in a first semiperipheral sector thereof and defining a second blank semiperipheral sector of said conduit extending longitudinally through said interval, each of said perforations defining a linear flow course for the flow of fluids into the interior of said conduit and being disposed such that at least one of said flow courses is oriented at an oblique angle with respect to a surface in the interior of said conduit and intersects another of said flow courses; and

a second conduit disposed in said well exteriorly of said first-named conduit and adjacent said second blank sector of said first conduit.

2. The assembly of claim 1 wherein at least some of said perforations are vertically spaced along said first conduit and extend through the wall of said first conduit at an oblique angle relative to the axis of said first conduit.

3. The assembly of claim 2 wherein the flow courses of an adjacentpair of.said vertically spaced perforations intersect each other before said flow courses of said adjacent perforations intersect said surface.

4. In a well penetrating the subterranean formation and adapted for the production of fluids therefrom, an assembly for alleviating erosion of downhole equipment comprising:

a first conduit disposed in said well;

a plurality of perforations in an interval of said first conduit in a first semiperipheral sector thereof and defining a second blank semiperipheral sector of said first conduit extending longitudinally through said interval, each of said perforations defining a linear flow course for the flow of fluids into the interior of said first conduit; and

a second conduit of smaller size than said first conduit eccentrically disposed within said first conduit and extending through said interval thereof adjacent said second blank sector of said first conduit, said perforations in said first conduit being vertically spaced and oriented at oblique angles relative to the axis of said first conduit so that the flow course from each perforation is intersected byat least one of the other of said flow courses prior to any of said flow courses reaching said second conduit whereby the linear flow of fluid following said flow courses intersects and becomes turbulent flow before impinging on said second conduit.

References Cited UNITED STATES PATENTS 1,313,875 8/1919 Borel --4.6 X 2,252,996 8/1941 Tow 175-4.58 2,304,408 12/ 1942 Holifield 1754.56 2,593,866 4/1952 Evans 175--4.57 2,873,676 7 2/1959 Caldwell 1754.6 2,947,250 8/ 1960 Mohaupt 1754.6 2,639,770 5/1953 Huber 1754.53 3,031,965 5/1962 Nelson 16655.1 X 3,104,710 9/1963 Pitts 16655.1 X 3,110,257 11/1963 Lebourg.

3,165,153 1/1965 Lanmon 166-35 X 3,172,469 3/1965 Coberly et a1. 16645 X FOREIGN PATENTS 664,197 6/1963 Canada.

DAVID H. BROWN, Primary Examiner. 

